Technical Field
This disclosure relates generally to linestops for temporarily shutting off flow in a pressurized pipe. More specifically, this disclosure relates to installation assemblies for such linestops that include a nozzle and a completion plug that may be used to install linestops in pipes of varying sizes.
Description of the Related Art
Pressurized pipes convey fluids, both liquid and gas, in municipalities, industrial plants, and commercial installations. When originally installed, these pipes include block valves used to isolate sections of the pipe for repairs, relocation, or installation of new components into the pipe. When a shutdown is required in a municipal water system, a large area may be deprived of water service. Accordingly, schools, hospitals, commercial and/or industrial facilities may have to be shut down in addition to the inconvenience to residents.
The length of pipe to be isolated during a shutdown can be shortened by adding additional plugs or linestops, in conjunction with the preexisting block valves. Linestops may be installed in a pressurized pipe without service interruption and with minimal fluid loss. If such a linestop is installed, upon completion of the work on the depressurized section of the pipe, the linestop can be retracted and the block valves opened, thereby restoring flow through the repaired section of pipe.
Typically, a linestop is installed through a housing that is clamped to the pressurized pipe that is known in the art as a nozzle or a nozzle assembly. In most cases, the nozzle includes a cylindrical housing section that is clamped perpendicular and pressure-tight to the outside of the pipe by a saddle assembly. Communication is established by a process called pressure tapping, hot tapping or under-pressure tapping. This process is well known in the art, and utilizes a temporary valve, such as a knife valve, mounted on the nozzle and a pipe tapping assembly mounted on top of the knife valve. The knife valve is opened to allow a cutting or drilling device from the pipe tapping assembly to be lowered through the knife valve and through the nozzle to cut a hole through the pipe without significant loss of fluid pressure or fluid flow. After the pipe is cut, the cutting device and coupon (i.e., the cut portion of the pipe) are withdrawn and the knife valve is closed. Then, the pipe tapping assembly is removed and a linestop installation assembly that includes a linestop is mounted on top of the knife valve. The knife valve is then opened and the linestop is lowered into place within the pipe and compressed to form a plug that stops flow through the pipe. After work on the pipe is complete, the linestop can be withdrawn through the knife valve and into the linestop installation assembly before the knife valve can be closed. Then, the linestop installation assembly is removed so the linestop can be replaced with a completion plug. Using the linestop installation assembly, the completion plug is passed through the knife valve before it is secured in place in the nozzle. With the completion plug in place in the nozzle, the linestop installation assembly and knife valve may be removed and replaced with a cover plate known in the art as a blind flange.
Two types of completion plugs are available. First, the completion plug and the nozzle may be threaded for threadably securing the completion plug in the nozzle. Second, the completion plug may be a push-in type of completion plug that is held in place within the nozzle by pins. Further, customers demand the availability of both types of completion plugs. As a result, both types of completion plugs must be manufactured for each size (ID) of pipe (i.e., typically four, six and eight inches), thereby requiring the manufacture of at least six different completion plugs.
The current method of manufacturing nozzles for linestops is labor intensive and includes significant machining and welding. Specifically, the nozzle includes a cylindrical housing that is welded to a flange at its distal end and welded perpendicularly to an upper saddle member at its proximal end after an opening is plasma cut in the upper saddle member. Welding the proximal end of the nozzle to the upper saddle member is difficult as the welding material is prone to seeping between the proximal or lower end of the nozzle and the upper saddle member. Further, pipes having a common internal diameter (ID), e.g., eight inches, may have varying outer diameters (ODs), depending on the thickness of the pipe, the material used to fabricate the pipe, the pressure rating and the end use. Currently, the size of the nozzle is varied for each pipe ID, not each pipe OD, but the size of the saddle assembly is varied for each pipe OD. As a result, the proximal end of the nozzle may not have a diameter that exactly matches that of the upper saddle member, which exacerbates the problem of welding material seeping between the proximal end of the nozzle and the upper saddle member. Further, nozzles are not typically able to accommodate both types of completion plugs and therefore as many as six different nozzles must be manufactured for the three common sizes of pipe (i.e., four, six and eight inches). It would be advantageous to provide a single nozzle for each pipe ID that could accommodate both types of completion plugs. Such a nozzle design would reduce the number of nozzles required for three different pipe IDs from six to three.
Other problems associated with nozzles for linestops include difficulties associated with installing the nozzles below ground level because the nozzles are not equipped with a structure that can be used to tether the nozzle to a winch. Further, the manufacture of the nozzles is expensive due to the amount of machining and welding that is required in addition to the six different nozzles that linestop installers must keep in stock to service four, six and eight inch pipe sizes.
Accordingly, improved nozzles and completion plugs are needed that may be used to install linestops in pressurized pipes.